Novak Djokovic of Serbia reacts during the men's singles second round match against Grigor Dimitrov of Bulgaria at the Madrid Open tennis tournamentin Madrid, on May 7, 2013. Djokovic lost 1-2. (Xinhua/Xie Haining)

British player Andy Murray returns the ball to German player Florian Mayer during their tennis match at the Madrid Open tennis tournament in Madrid on May 7, 2013. Murray won 2-0 and advanced to the next round. (Xinhua/Xie Haining)

German player Florian Mayer throws his racket during the men's singles second round match against British player Andy Murray at the Madrid Open tennis tournament in Madrid on May 7, 2013. Murray won 2-0 and advanced to the next round. (Xinhua/Xie Haining)

Novak Djokovic of Serbia reacts during the men's singles second round match against Grigor Dimitrov of Bulgaria at the Madrid Open tennis tournament in Madrid, on May 7, 2013. Djokovic lost 1-2. (Xinhua/Xie Haining)

German player Florian Mayer returns the ball to British player Andy Murray during their match at the Madrid Open tennis tournament in Madrid on May 7, 2013. Murray won 2-0 and advanced to the next round. (Xinhua/Xie Haining)

Novak Djokovic of Serbia reacts during the men's singles second round match against Grigor Dimitrov of Bulgaria at the Madrid Open tennis tournament in Madrid, on May 7, 2013. Djokovic lost 1-2. (Xinhua/Xie Haining)

(130508) -- MADRID, May 8, 2013 (Xinhua) -- Novak Djokovic of Serbia returns the ball during the men's singles second round match against Grigor Dimitrov of Bulgaria at the Madrid Open tennis tournament in Madrid, on May 7, 2013. Djokovic lost 1-2. (Xinhua/Xie Haining)

(130508) -- MADRID, May 8, 2013 (Xinhua) -- British player Andy Murray returns the ball to German player Florian Mayer during their tennis match at the Madrid Open tennis tournament in Madrid on May 7, 2013. Murray won 2-0 and advanced to the next round. (Xinhua/Xie Haining)

Grigor Dimitrov of Bulgaria reacts after winning the men's singles second round match against Novak Djokovic of Serbia at the Madrid Open tennis tournament in Madrid on May 7, 2013. Dimitrov won 2-1. (Xinhua/Xie Haining)

Grigor Dimitrov of Bulgaria reacts after winning the men's singles second round match against Novak Djokovic of Serbia at the Madrid Open tennis tournament in Madrid on May 7, 2013. Dimitrov won 2-1. (Xinhua/Xie Haining)

Grigor Dimitrov of Bulgaria reacts after winning the men's singles second round match against Novak Djokovic of Serbia at the Madrid Open tennis tournament in Madrid on May 7, 2013. Dimitrov won 2-1. (Xinhua/Xie Haining)